Backport PR matplotlib#31975: pdf/ps: Stop retaining glyph indices in font subsets

Author: ksunden

ci/minver-requirements.txt

@@ -2,7 +2,7 @@
 
 contourpy==1.0.1
 cycler==0.10
-fonttools==4.22.0
+fonttools==4.28.2
 importlib-resources==3.2.0
 kiwisolver==1.3.2
 meson-python==0.13.2

doc/install/dependencies.rst

@@ -24,7 +24,7 @@ reference.
 * `contourpy <https://pypi.org/project/contourpy/>`_ (>= 1.0.1)
 * `cycler <https://matplotlib.org/cycler/>`_ (>= 0.10.0)
 * `dateutil <https://pypi.org/project/python-dateutil/>`_ (>= 2.7)
-* `fontTools <https://fonttools.readthedocs.io/en/latest/>`_ (>= 4.22.0)
+* `fontTools <https://fonttools.readthedocs.io/en/latest/>`_ (>= 4.28.2)
 * `kiwisolver <https://github.com/nucleic/kiwi>`_ (>= 1.3.1)
 * `NumPy <https://numpy.org>`_ (>= 1.25)
 * `packaging <https://pypi.org/project/packaging/>`_ (>= 20.0)

environment.yml

@@ -15,7 +15,7 @@ dependencies:
   - cxx-compiler
   - contourpy>=1.0.1
   - cycler>=0.10.0
-  - fonttools>=4.22.0
+  - fonttools>=4.28.2
   - importlib-resources>=3.2.0
   - kiwisolver>=1.3.1
   - pybind11>=2.13.2

lib/matplotlib/backends/_backend_pdf_ps.py

@@ -4,6 +4,7 @@
 
 from __future__ import annotations
 
+from contextlib import contextmanager
 from io import BytesIO
 import functools
 import logging
@@ -18,6 +19,9 @@
 
 
 if typing.TYPE_CHECKING:
+    from collections.abc import Generator
+    from contextlib import AbstractContextManager
+
     from .font_manager import FontPath
     from .ft2font import CharacterCodeType, FT2Font, GlyphIndexType
     from fontTools.ttLib import TTFont
@@ -35,7 +39,30 @@ def _cached_get_afm_from_fname(fname):
         return AFM(fh)
 
 
-def get_glyphs_subset(fontfile: FontPath, glyphs: set[GlyphIndexType]) -> TTFont:
+class SubsetResults(typing.NamedTuple):
+    """
+    The results of a subsetting operation on a font.
+
+    Attributes
+    ----------
+    font : TTFont
+        An open font object representing the subset.
+    glyph_index_map : dict
+        Mapping of requested glyph indices to actual subset glyph indices.
+    """
+
+    font: TTFont
+    glyph_index_map: dict[GlyphIndexType, GlyphIndexType]
+
+    @contextmanager
+    def _as_cm(self) -> Generator[SubsetResults, None, None]:
+        with self.font:
+            yield self
+
+
+def get_glyphs_subset(
+    fontfile: FontPath, glyphs: set[GlyphIndexType]
+) -> AbstractContextManager[SubsetResults]:
     """
     Subset a TTF font.
 
@@ -50,12 +77,10 @@ def get_glyphs_subset(fontfile: FontPath, glyphs: set[GlyphIndexType]) -> TTFont
 
     Returns
     -------
-    fontTools.ttLib.ttFont.TTFont
-        An open font object representing the subset, which needs to
-        be closed by the caller.
+    SubsetResults
+        The font and new glyph index mapping.
     """
-    options = subset.Options(glyph_names=True, recommended_glyphs=True,
-                             retain_gids=True)
+    options = subset.Options(glyph_names=True, recommended_glyphs=True)
 
     # Prevent subsetting extra tables.
     options.drop_tables += [
@@ -87,7 +112,7 @@ def get_glyphs_subset(fontfile: FontPath, glyphs: set[GlyphIndexType]) -> TTFont
     subsetter = subset.Subsetter(options=options)
     subsetter.populate(gids=glyphs)
     subsetter.subset(font)
-    return font
+    return SubsetResults(font, subsetter.glyph_index_map)._as_cm()
 
 
 def font_as_file(font):

lib/matplotlib/backends/backend_pdf.py

@@ -1247,7 +1247,7 @@ def embedTTFType42(font, subset_index, charmap, descriptor):
             _log.debug("SUBSET %r:%d characters: %s", filename, subset_index, charmap)
             with _backend_pdf_ps.get_glyphs_subset(filename,
                                                    charmap.values()) as subset:
-                fontdata = _backend_pdf_ps.font_as_file(subset)
+                fontdata = _backend_pdf_ps.font_as_file(subset.font)
             _log.debug(
                 "SUBSET %r:%d %d -> %d", filename, subset_index,
                 os.stat(filename).st_size, fontdata.getbuffer().nbytes
@@ -1290,7 +1290,8 @@ def embedTTFType42(font, subset_index, charmap, descriptor):
             cid_to_gid_map = ['\0'] * 65536
             widths = []
             max_ccode = 0
-            for ccode, gind in charmap.items():
+            for ccode, orig_glyph_index in charmap.items():
+                gind = subset.glyph_index_map[orig_glyph_index]
                 glyph = font.load_glyph(gind,
                                         flags=LoadFlags.NO_SCALE | LoadFlags.NO_HINTING)
                 widths.append((ccode, cvt(glyph.horiAdvance)))

lib/matplotlib/backends/backend_ps.py

@@ -190,12 +190,13 @@ def _font_to_ps_type42(font_path, subset_index, glyph_indices, fh):
         with (fontTools.ttLib.TTFont(font_path.path,
                                      fontNumber=font_path.face_index) as font,
               _backend_pdf_ps.get_glyphs_subset(font_path, glyph_indices) as subset):
-            fontdata = _backend_pdf_ps.font_as_file(subset).getvalue()
+            new_font = subset.font
+            fontdata = _backend_pdf_ps.font_as_file(new_font).getvalue()
             _log.debug(
                 "SUBSET %s:%d %d -> %d", font_path, subset_index,
                 os.stat(font_path).st_size, len(fontdata)
             )
-            fh.write(_serialize_type42(font, subset_index, subset, fontdata))
+            fh.write(_serialize_type42(font, subset_index, new_font, fontdata))
     except RuntimeError:
         _log.warning(
             "The PostScript backend does not currently support the selected font (%s).",